When presses, machine tools, construction machines, ships, aircrafts, unmanned couveying units, unmanned warehouses or the like are to be centrally controlled, a large number of sensors for detecting the present operative state of each section in these machines or installations and a large number of actuators for controlling the present operative state of each section in these machines or installations are required. For example, in the case of a press, the number of required sensors and actuators exceeds 3000. In other case, each machine or installation may need to be equipped with sensors and actuators more than 3000 in number.
Hitherto, the central control system for centrally controlling the foregoing kinds of machines or installations is typically constructed such that a number of sensors and a number of actuators are connected to a main controller so that a number of sensor outputs are collected in the main controller which in turn controls the actuators.
With the conventional central control system as constructed in the above-described manner, as a large number of sensors and actuators are required, the number of connection lines extending between the main controller and the sensors/actuators increases enormously. In addition, an input/output section in the main controller becomes unavoidably complicated in structure.
To obviate the foregoing problem, a proposal has been made such that a plurality of nodes are serially arranged one after another, one or a plurality of sensors and actuators are connected to each node and the nodes are connected to each other via a main controller so that each node is properly controlled in response to a signal outputted from the main controller. With such a structure as described above, the main controller is basically required to have a plurality of signal input lines and a plurality of signal output lines by way of which the main controller is connected to the respective nodes, resulting in the number of wiring lines being reduced substantially.
However, in a case where the central control system is constructed such that the nodes are serially connected to each other, there arises a problem as to how simultaneous collection of outputs from the respective nodes and simultaneous control of the respective actuators are accomplished. For example, in the case of a structure wherein a specific address is allocated to each node to control the latter based on the allocated address, time delay caused by processing a plurality of allocated addresses becomes another problem. Thus, simultaneous collection of outputs from the respective sensors and simultaneous control of the respective actuators cannot be accomplished satisfactorily.
In view of the aforementioned facts, the inventors abandoned the technical concept that a plurality of nodes are serially connected to each other with a specific address allocated to each node. Instead of the foregoing technical concept, the inventors propose a serial control apparatus which is constructed such that each node is distinguished from other node in accordance with an order of node connection. With this proposed serial control apparatus, any address processing is not required and time delay caused by the address processing is eliminated with the result that a node structure can be simplified remarkably.
The proposed serial control apparatus is constructed such that each node successively adds output signals from sensors in the present node to a signal from nodes on the upstream side in compliance with a predetermined rule and signals specifically intended for the present node are successively extracted from among signals transmitted from nodes on the upstream side so that the former signals are outputted to a plurality of actuators associated with the present node. With the serial control apparatus, each node does not require not only any address but also a step of address processing, causing time delay at each node to be reduced to such a very small quantity that merely a timing coincidence is required. Additionally, a node structure is largely simplified.
FIG. 1 is a block diagram which schematically illustrates by way of example the aforementioned serial control apparatus. As is apparent from the drawing, the serial control apparatus includes a main controller 2 and n nods 3 - 1 to 3 - n both of which are arranged along a loop-shaped signal transmission line 1, and each of the nodes 3 - 1 to 3 - n has a plurality of sensors Sl to Si and a plurality of actuators Al to Ak connected thereto.
As shown in FIG. 2(a), the main controller 2 sends a communication information to the signal transmission line, wherein the communication information includes a start code ST at the head end, a control information DATA for each node at the subsequent location, a stop code SP indicative of the end of the control information DATA at the subsequent location and an error check code ERC such as a parity check code, a CRC code or the like at the tail end. The communication information is serially transmitted to the respective nodes 3 - 1 to 3 - n via the signal transmission line 1.
When each of the respective nodes 3 - 1 to 3 - n receives a communication information via the signal transmission line 1, it extracts a control information on a time slot corresponding to a specific connection number allocated to the present node and then controls the actuators Al to Ak in accordance with the control information. Then, each node inserts output signals for the sensors Sl to Si into a time slot associated with the connection number allocated to the present node, and the output signals are transmitted to nodes on the downstream side.
Therefore, when the control information DATA transmitted from the main controller 2 is outputted from the node 3 - n on the ultimate downstream side (see FIG. 2(e)), it is converted into a sensor output signal for each node. In response to the sensor output signal, the main controller detects the present operative state of each of the nodes 3 - 1 to 3 - n. Then, the process goes to a next control step.
Referring to FIG. 2 again, T.sub.01, T.sub.02, T.sub.11, - - - represent a signal transmission time of the corresponding signal, respectively. With the illustrated serial control apparatus, it is assumed that transmission of a series of signals S0 to Sn shown in FIG. 2 is repeatedly carried out at a high speed in accordance with the following relationship. ##EQU1##
When such a serial control apparatus as described above is employed, a signal frame as shown in FIG. 2 is used as a signal to be transmitted through the respective nodes 3 - 1 to 3 - n and moreover the aforementioned protocol is additionally employed for the serial control apparatus. Thus, data receiving/transmitting and error check can certainly and effectively be accomplished with the serial control apparatus. However, in a case where a certain machine is to be controlled with the serial control apparatus via, e.g., a plurality of actuators as mentioned above, there is liable to arise a malfunction that informations are erroneously outputted to the actuator and thereby incorrect operation of the machine to be controlled is induced.
The present invention has been made with the foregoing background in mind and its object resides in providing a data extracting circuit employable for a serial control apparatus which can reliably prevent a plurality of actuators or the like from being erroneously actuated and moreover assures that a machine to be controlled is properly operated with a high reliability.